1. Field of the Invention
The present invention is directed to a medical examination installation with an MR system and an X-ray system that has an X-ray radiator with an X-ray tube and a solid-state X-ray image detector for producing X-ray exposures.
2. Description of the Prior Art
Real-time monitoring of interventional medical procedures is necessary, in order to ensure that the procedure is proceeding as intended, and as well as to ensure that any medical instruments which are being employed are precisely positioned at the correct location in the patient.
Magnetic resonance (MR) imaging is a proven diagnostic method that enables tomograms and three-dimensional (3D) reconstructions to be produced. The examination time, however, is relatively long and lies on the order of magnitude of several minutes. For specific examinations, it is meaningful for shortening the exposure time and/or for planning the further execution of the MR examinations to prepare an X-ray exposure before and/or during the MR examination. The quality of the diagnosis is additionally enhanced as a result.
Although such MR systems can fundamentally make the 3D location information required therefor available, there are situations wherein it is desirable to have better access to the patient during the intervention than that afforded by the gantry of an MR system with superconductive magnet or even by a C-shaped magnet apparatus (open). When the patient is moved out of the gantry of the inner magnet region of the MR apparatus for the time of the intervention, for example, an open surgical intervention or the introduction of a biopsy needle can be enabled or simplified. Moreover, monitoring of the patient is improved in this way, for example the delivery of respiratory gasses, infusion tubes as well as a general monitoring of the condition of the patient.
However, organs can dislocate in the intervention due to the pressure of an interventional or surgical tool such as, for example, a biopsy needle or a catheter, so that the current organ position can deviate from the position at the earlier point in time of an MR image acquisition.
For these reasons, it is advantageous when an additional X-ray systemxe2x80x94optimally with real-time image acquisition in the fluoroscopic mode or during transilluminationxe2x80x94is integrated in an MR apparatus so that a relationship of the local information between the acquired X-ray images to the MR images is possible. An intervention with enhanced certainty thus is possible without delay and with the involvement of the images of both modalities. It is especially advantageous when the X-ray system can make images with 3D information available that can be correlated with the MR images.
PCT Application WO 96/00520 discloses a medical examination installation with an MR system and an independent X-ray system wherein an Independent X-ray device is provided in addition to an Independent MR device. The X-ray device has a voltage supply as well as a C-arm with an X-ray source and the X-ray detector, which form an X-ray unit. A patient lying on a patient support is transported back and forth between the MR device and the X-ray device. The X-ray detector can be a large-area solid-state image converter.
Conventional X-ray real-time image systems with X-ray tubes can be employed only conditionally at MR systems because the stray magnetic field of the MR apparatus does not allow a disturbance-free operation of the X-ray tubes, even though the magnetically deflectable electrons exhibit high speeds over short oath distances.
In the aforementioned POT Application WO 96/00520, for example, it is taught to align the electron path in the X-ray tube according to the magnetic field lines in the proximity of the MR magnet. This alignment of the electron oath functions only at a fixed distance of the MR apparatus from the X-ray tube because the angle of the magnetic field lines changes with the distance from the MR apparatus. Additionally, the tilt of the axis of the X-ray tube relative to the axis of the MR apparatus reduces the usable emission angle of the X-ray tube, and thus the field of view.
An object of the present invention is to provide a medical diagnostics installation such that an online X-ray system is possible directly at the MR apparatus without influencing the electron oath in the X-ray tube with the magnetic field lines of the MR magnet even given changes in the position or attitude of the X-ray tube.
This object is inventively achieved in a medical examination installation having sensors which identify the magnetic, location-dependent stray field of the MR system in the three spatial axes, a computer determines the coil currents, and coils operated by the computer which compensate the stray field.
It has proven advantageous for the X-ray system to have magnetic field sensors for acquiring the magnetic, location-dependent stray field of the MR system in the three spatial axes.
The magnetic stray field can already be reduced when the X-ray system has a magnetic shielding for the X-ray tube within which the sensors for acquiring the location dependency of the remaining magnetic stray field and within which the coils are arranged.
It has proven advantageous to employ three coil pairs arranged such that their axes respectively reside perpendicularly relative to one another, the coil pairs being arranged in the three spatial axes.
Alternatively, the sensors for the acquisition of the location dependency of the stray field of the MR system in the three spatial axes can be location sensors that determine the position of the X-ray tube in view of the MR system and calculate the magnetic, location-dependent stray field of the MR system at the location of the X-ray tube on the basis of stored magnetic field profiles.
A compact structure derives when the X-ray system is directly attached to the MR apparatus, and the X-ray radiator and the solid-state image detector can be mounted to a C-arm attached to the MR system. The X-ray system alternatively can be mounted to stands directly next to the MR apparatus.
As an alternative, the X-ray radiator and the solid-state X-ray image detector can be secured independently of one another, with location sensors for determining position and angle attached to the X-ray radiator and the solid-state X-ray image detector. The X-ray radiator and the solid-state X-ray image detector are aligned relative to one another and readjusted by motor drives and electronic controls. The position and alignment of X-ray radiator and solid-state X-ray image detector are monitored by the location sensors, so that a so-called xe2x80x9celectronic C-arm is achieved. The measurement sensor mechanism with path sensors and rotational angle sensors assures that the current, exact position of the X-ray system in relation to the MR apparatus, particularly relative to the position of the patient support thereof and of the individual components relative to one another is known, so that the components can be reliably and precisely moved on the desired paths.
Spatial information of tomosynthesis images can be linked with the content of stored MR images according to the image fusion technique when the X-ray system is fashioned such that, for producing exposures from a number of projections for tomosynthesis tomograms, X-ray radiator and/or solid-state X-ray image detector are moved on a plane parallel thereto, and when the workstation is configured such that the tomosynthesis tomograms and MR images are superimposed.
It has proven advantageous when the solid-state X-ray image detector is arranged to be displaceable in the patient support.